Impact mill with centrifugal separation



Jan. 14, 1947. CQWLES 2,414,361

IMPACT MILL WITH CENTRIFUGAL SEPARATION Filed Dec. 31, 1942 2 Sheets-Sheet 1 INVENTOR wad?- E -754% Jan. 14, 1947. E. COWLES 2,414,361

IMPACT MILL WITH CENTRIFUGAL SEPARATION Filed Dec. 31, 1942 2 sneak-sheet 2 INVENTOR Patented Jan. 14, 947

UNITED STATES ATENT' OFFICE nursc'r MILL wrrn CENTRIFUGAL snmnn'rron Edwin Cowles, Cayuga, E, assignm- The Cowles tion of New Jersey Company, Princeton, N. .L, a corpora Application December 31, 1942, Serial N0. 470,731 2 Claims. (on. 241-55) This invention relates comminuting, triturating or otherwise reducing to mills for pulverizing, v

the size of pieces of solid material, preferablyto a I lected for purposes of illustration is shown in the accompanying drawings, in which,

Figure 1 is a front elevation, with the front wall partly broken away, and partly in section on the line -l, of Figure 2. v

Figure 2 is a side elevation, with the side wall partly broken away, and partly in section on the' line 2-2 of Figure 1.

Figures 3 and 4 are similar views of a modified form, the sectioned portion of Figure 3 being on the line 3-3 of Figure 4, and the sectioned portion of Figure 4 being on the line 8-4 of Figure 3.

Referring to Figures 1 and 2 of the drawings, the apparatus comprises a casing I having a front wall 2, a rear wall 82, and a cylindrical shell 33 therebetween. The casing is designed for easy and rapi'dassembly and disassembly, and for this purpose is carried on a frame 4 having a face plate 34 to which the component parts of the casing are secured by means of bolts 35. The frame also servesas a support for the shaft 5, said shaft being carried in bearings (not shown) in a housing 6 forming an integral part of the frame. The shaft may be driven in any suitable manner, as by a pulley I mounted onone end thereof. The other end of the shaft extends into the casing, and carries a grinding material secured thereto as hereinafter described and adapted to rotate therewith.

In the preferred embodiment illustrated the said grinding member comprises a plurality of grinder bars 8 having peripheral grinding surfaces 9. The said bars are welded or otherwise secured to annular rings H and I2, and the resulting assembly may be secured by bolts l3 to a flanged hub l4 secured to the shaft by a nut i5.

The interior of the casing, opposite the peripheral grinding surfaces, is spaced from said surfaces, but is provided with spaced bars It held in groovesjin the shell 33, and extending transversely across the casing, which said bars are also spaced from the grinding surfaces.

. In the embodiment illustrated, the bars 8 are somewhat larger than necessary to provide ade-' quate structural strength, in order that the inner part of said bars may serve as vanes or paddles tending to whirl the-material in the chamber between the grinding surfaces and the discharge opening 3 through which the ground material is discharged. Said vanes establish and maintain a centrifugal separating action in said chamber tending to return the larger pieces of material to the zone of grinding action and allowing only the more finely ground material to be discharged. Thus, in addition to their grinding function, the

bars 3 are constructed and arranged so that part of said bars may perform the functions of thecentrifuging vanes of my copending application above referred to. V

In this connection, the stationary bars 16 may again be referred to. It will be observed that the arrangement of the said bars is such as to retard the movement of material along the inner wall of the shell 33, so that the material in what may be called the grinding zone, 1. e., the space between the grinding surfaces 9 and the inner'wall of the casing, does not partake of the whirling movement of the material in what may b called the centrifuging'zone, i. e., the space or chamber between the grindingsurfaces and the outlet opening. Thus there is an effective separation of the two operations of grinding and centrifugal separation or selection, and such separation improves the effectiveness of both operations. For example, it will be understood that thegrinding action' is partly due to impact and partly due to attrition. By retarding the movement of the material in the grinding zone, not only is the impact of the rotating bars on the retarded material greater than would be the case if that material .were moving more rapidly, but also the impact of the material rebounding from the rotating bars against the retarded material is greater than if that material were moving more rapidly. Similarly, of course, the attrition effect between the rotating bars and retarded material is greater 'than if the materialdn the grinding zone were moving more rapidly.

The bars 8 are also arranged, as shown, in such manner that their front faces are inclined to a radius passing therethrough in such manner that the inner portions are advanced. This has the effect of restricting the passage between adjacentbars, thus tending to trap the larger pieces and prevent them from moving toward the discharge opening until further reduced in size. It also has the effect of causing pieces of material which are struck by the advancing faces of the bars to move outwardly rather than inwardly toward the on.

charge opening. 7

In the preferred embodiment illustrated a pair the bars where the centrifugal action is least effective. If desired the bars 8 may be provided with notches 88 registering with annular projections 48 on the rings 81, 88 which further impose, thering'tl' may be provided with a plu-. rality of stationary fins 48 which reduce the proves the restraining action by causing any fiected by the projections 88 into the path of the vane portions of the bars 8. It will-be understood that the casingwalls 2 and 82 might be arranged to have a loose running fit with the ends of the bars I and thus serve the purpose of the rings 81. 88. I-Iowever.'considerable wear occurs due to abrasion and the rings are easily replaceable as wear occurs. v

In the operation of the machine, material to be ground is fed into the machine through the inlet passage II in the wall of the shell 33, said passage being arranged substantially tangentially to the path of the bars 8. Since the action of the vane portions of the bars 8 acting alone would 'tend to pump air backwardly so as to discharge partially ground material through the inlet passage, the machine is used in combination with a blower to circulate air through the machine toward the discharge opening. 8

In operation, the grinding member is preferably rotated at velocities considerably lower than described in my copending application before referred to, the particular velocity selected depending on the nature of the material and the particle size desired. For example, good results may be secured in grinding easily frangible materials at I particles which tend to move inwardly to be de-' and projection 40' to further improve. the restraining action.

Stationary'bars it are also provided in the modified form ofmachine and serve the same purposes as in the form shown in- Figures 1 and v2.

However, because of the wide separation between the grinding zone and the centrifuging zone in the modified form it is advisable in some cases to provide additional means to retard whirling movement between the two zones. For this purwhirling in the chamber and hence reduce the centrifugal separating eilect within their zone of effective action, and particularly at the entrance to said passage. Thus the principal centrifugal effect is' exerted by the vanes 28 of the rotating member, but also on the velocity of the current of air induced by said blower. The higher the velocity of the latter, the larger will be thesize of the particles discharged. assuming that the velocity of the rotating member remains the same. Thus, by balancing the velocity of the rotating member against'the velocity of the current of air, the particle size discharged may be controlled. I I

A modified form of machine is shown in Figures 3 and 4 in which the grinder bars 8' having grinding surfaces 8' are of a size merely sufflcient to provide adequate structural strength, 'and alone.

. Themodified form of machine of Figures 8 and 4 is designed to be capable of operation at velocities higher than those of the machine of Figures 1 and 2. The machine is thus available for use in grinding materials which require more.

severe attrition or heavier impact in order to be reduced to the desired particle size. In both the machine of Figures 1 and 2 and the machine of Figures 3 and 4 it will be understood that the higher the velocity, the greater the centrifugal effect, and in the machine of Figures 1 and 2 when the machine is'run at velocities sufllciently high to secure emcient grinding of certain materials, the centrifugal effect is so great that the discharged particle size is too small. In the machine of Figures 3' and 4, however, the arrangement is such as to permit the use of higher velocities while at the same time reducing the centrifugal effect by locating the centrifuging vanes nearer'to the axis of rotation. Thus by properselection of machine, velocity of rotating member, velocity of air flow and vane locations,

a, wide range 'of materials may be reduced to faces'toward said discharge opening to centrifuge the same, said vanes having notches formed in deflect ground material moving between the ends hence exert little or no centrifugal selecting ef-,

fact. In this form of machine, therefore. sepa-' extends somewhat closer to the discharge open-- ing 8' and has a loose rlmning fit withthe edges of the vanes 28 in order to restrain the passage of material toward the discharge opening along the edges of the vanes. As before, the vanes and ring may be provided with registering notches 88' of said vanes and saidcasing toward said discharge opening into the path of said vanes.

2. A mill comprising a casing,. a grinding member mounted forrotation in said casing, saidgrinding member having a plurality of grinder bars having. peripheral grinding surfaces spaced from the surrounding wall of the casing to Provide a grinding zonetherebetween, said grinder bars being spaced to provide passages therebetween through which ground material may move-from the grinding zone toward the axis of rotation of said member, stationary bars ing surfaces of said grinder bars and projecting ing across the space providing communication therebetween serving as vanes to whirl all of the ground material moving between said bars toward said discharge opening to subject the same' to substantially uniform centrifuging action, the

I front faces of said grinder bars being inclined in such manner that the inner portions are advanced.

EDWIN COWLES. 

